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Fried CMUcam — Parallax Forums

Fried CMUcam

maxxmaxx Posts: 14
edited 2006-01-05 19:48 in BASIC Stamp
Hi everybody,

I was doing some demos using my CMUcam and the Basic stamp board of education. But unforunately I reversed the voltage polarities by accident shakehead.gif . Is there any way that I can fix it myself. And I wonder which part specificaly did I fry. Thanx for your help

Comments

  • maxxmaxx Posts: 14
    edited 2005-12-15 23:59
    I would like to add that when I applied the reversed polarity it didn't last longer than 20 seconds max. I realized my mistake quickly and I unplugged it and when I plugged it back the green light was gone and it's doesn't any longer respond to any of the old programs. In fact it doesn't respond at all cry.gif
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2005-12-16 03:10
    A full-wave bridge would've prevented that.
  • LarryLarry Posts: 212
    edited 2005-12-16 04:51
    Bad news is, you probaly fried the SX chip. The good news is you can get another reflashed with the firmware from Seattlerobotic.com (maybe from Acroname, too )

    Tell them what you did. It shouldn't cost more than $10 or so plus shipping.

    Your not the first one to do it. I got lucky and just fried the voltage regulator. In fact, see if the regulator is still putting out 5v, first

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  • maxxmaxx Posts: 14
    edited 2005-12-16 19:50
    Thanx for your advice. I'll check my voltage regulator first before i order the sx chip
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-12-16 20:29
    Most regulators are designed to sacrifice themselves before passing bad voltages downstream to potentially more sensitive devices. Most of the new breed regulators have internal protection against overvoltage/overcurrent/and wrong polarity. As mentioned check the regulator, if you are good at soldering you can replace the regulator yourself, and perhaps get a package and pin compatible regulator that has the extra protection in case you do it again.

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    ·1+1=10
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2005-12-16 22:41
    · The full-wave bridge prevents reverse bias, always.· As a matter of fact,·no matter what·the "polarity" of the input voltage, the output is always there.

    · Please use rectifier diodes (1N4001, 1N4002, &c.)·

    · [noparse][[/noparse] But it only works when the supply always runs through it. ]

    · Drawing attached.
    FWB.jpg
    494 x 299 - 13K
    FWB.jpg 12.8K
  • LarryLarry Posts: 212
    edited 2005-12-17 02:31
    It is pretty foolproof. The downside is that you loose about .7 volts for each diode that passes current. If you have the camera on a robot. the minimum battery voltage would probably have to be above 8 volts.

    You can just put a diode on the ground side to prevent reverse voltage. That saves you one of the .7 volt drops.

    The slick way to do it is to use a PNP FET with the drain to positive battery, the gate to negative battery, and the source to the regulator. Almost no voltage drop. and the FET won't pass any current if there is a positive voltage on what should be the battery ground

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  • maxxmaxx Posts: 14
    edited 2005-12-31 19:18
    Hello Everybody,
    Happy New Year. I went back to my CMU cam 1 and i checked the regulator and it looks fine to me. The output voltage was 5v and the input was 6.6v. I think the faulty part is the micro controller the sx28ac as The red LED is on but the green LED is always off and when i programed it doesn't respond. I wonder if i can reprogram the sx28ac or do i have to buy a new one?!. Once again guys Happy New Year and hope all your wishes come true in 2006.
  • HiTekGizmosHiTekGizmos Posts: 14
    edited 2006-01-03 16:58
    A full wave bridge is a BAD idea as it floats the ground reference above power ground. A better, proven approach is a reverse polarity protection diode. You install this diode ACROSS the power supply lines, so that it is reverse biased under normal operating conditions. When you hook the power up 'bass-ackwards' the power flows thru the diode to ground blowing the protective fuse and, hopefully, protecting the other circuitry... Really common in auto sound equipment, communications equipment, etc. Also note you do not loose the 0.7 volts typical of using a series pass diode... Fuses are cheap...
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-01-04 16:11
    HiTekGizmos said...
    A full wave bridge is a BAD idea as it floats the ground reference above power ground.
    Why is it "BAD"?· Ground reference "floats" above power ground when used as an AC rectifier, too, Yes?·
    So far as the "reverse diode as a high-current reverse-current path·and blow the fuse" idea goes -- wall-warts don't have fuses and batteries don't like run-away current that way either.·
    Nobody is really interested in any of these "solutions" anyway, it's always with the·live without a net stuff because fuses are 3 for $1 and that's too much money.· All most anybody wants to know is·how to set the "power protection bit" on their STAMP.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-01-05 19:48
    This is a product of Seattle Robotics and you may need to purchase a replacement part through them.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
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